1. Field of the Invention
The present invention relates to an optical printer head using plural light emitting devices, or image sensor or other array using plural photo detectors, and apparatus for printing or reading using the array, method of manufacturing the array, and method of mounting the array.
2. Description of the Prior Art
A typical prior art is shown in FIG. 1. In plural light emitting diodes A1, A2, . . . , light emitting regions 1P1 to 1P64, 2P1, 2P2, . . . are neatly arranged in one row. The arrays A1, A2, . . . arranged in one row are used by 40 arrays when the printing paper size is A4 format of the Japanese Industrial Standard and the printing dot density is 300 dots/inch, and the total number of light emitting regions is 2,560 dots. When printing by using such arrays A1, A2, . . . first the light emitting devices are selectively energized to emit light, and a preliminarily charged photosensitive drum is illuminated with light to write an electrostatic latent image. Next, in the developing process, the toner is deposited on the electrostatic latent image portion of the photosensitive drum to develop. Then, the image is transferred to the paper, and is fixed and thus printing is completed.
What is most important here is to mount the arrays A1, A2, . . . precisely on the electric insulating substrate. The printing quality depends on the mounting precision of the arrays A1, A2 installed and arranged as shown in FIG. 2. In other words, for maintaining the printing quality, the interval W between the light emitting regions 1P64 and 2P1 in FIG. 2 must be equal, as much as possible, to the pitch W1 between the remaining light emitting regions 1P1 and 1P64, and 2P1 and 2P64, and it is also important to control the value of deviation d of the vertical direction (the perpendicular direction in FIG. 1 and FIG. 2) with respect to the arranging direction of the arrays A1, A2 (the lateral direction in FIG. 1 and FIG. 2). In particular, the interval W influences the printing quality very much.
Hitherto, an automatic chip mounting device has been used for mounting the arrays A1, A2, . . . which are light emitting diode chips onto a substrate, and the shape of the front face of each array is taken by the television camera, and its image is processed by a computer, and the shape of the array is recognized, and the arrays are positioned and mounted on the predetermined positions on the substrate. By reading the positioning mark of the previously mounted array and the positioning mark of the newly mounted array, and calculating automatically, the arrays are mounted in a linear arrangement. As the positioning mark, in the prior art in FIG. 1, some of the wire bonding pads 1Q1 to 1Q64 to which the electrodes of the light emitting diodes are attached, together with the light emitting regions 1P1 to 1P64, are advantageous since they are made of aluminum and high in reflectivity and hence likely to be imaged, and the practical position recognizing method is to recognize the wire bonding pad 1Q1 (2Q1 in array A2) and wire bonding pad 1Q63, and the center is determined by calculation. These wire bonding pads 1Q1, 1Q63 are longer in the arranging direction (the lateral direction in FIG. 1) as compared with the remaining wire bonding pads 1Q2 to 1Q62, 1Q64, so that they may be recognized easily.
What matters here is that the pitch W1 of the light emitting regions 1P1 to 1P64, 2P1, 2P2, . . . varies between the arrays A1, A2 as indicated by reference W in FIG. 3. More specifically, every time the arrays A1, A2 are mounted, the interval W of the light emitting region varies in a certain fluctuation range. Thus, when the interval W varies, the following adverse effects are brought about to the printing quality. FIG. 3 (1) shows that the arrays A1, A2 are mounted correctly, with the interval W equal to the pitch W1, and accordingly, as shown in FIG. 4 (1), by drawing oblique lines, the print showing each dot is made normally. By contrast, as shown in FIG. 3 (2), in the case that the interval W between the light emitting regions 1P64 and 2P1 of the mutually adjacent arrays A1, A2 is less than the pitch W1, printing is done as shown in FIG. 4 (2), and near the region B1 corresponding to the interval W, the density is higher than in the surroundings, and black streaks are formed on the printing paper. Or, as shown in FIG. 3 (3), in the case that the pitch W between the light emitting regions 1P64 and 2P1 of adjacent arrays A1, A2 is over the pitch W1, as shown in FIG. 4 (3), the density is lower than in the surroundings in the region B2 corresponding to the interval W, so that white streaks are formed on the recording paper. In FIG. 4, meanwhile, printing dots on the recording paper by light emitting regions are indicated by drawing oblique lines.
Therefore, depending on whether the interval W is small or large, black streaks or white streaks are formed on the recording paper, and hence this interval W is very important for the printing quality. The limit of the size of the interval W not adversely affecting the printing quality is within .+-.10 .mu.m. Meanwhile, this pitch W1 is constant, for example, at 84.6 .mu.m.
The mounting precision of the interval W between the light emitting regions 1P64 and 2P1 of the mutually adjacent arrays A1, A2 is attributable to both the automatic mounting device of the arrays A1, A2 on the substrate, and the positional deviation of the light emitting region and positioning mark. The problem intended to be solved by the invention is related to the positional deviation of the positioning mark with respect to the light emitting region. As this positioning mark, the bonding pads 1Q1, 1Q63 are used. Such bonding pads 1Q1 to 1Q64 are different in process from the light emitting regions 1P1 to 1P64, and therefore when manufacturing this array A1, a mutual positional deviation occurs between the bonding pads 1Q1 to 1Q64 and the light emitting regions 1P1 to 1P64. Therefore, when the arrays A1, A2 in the position deviated state between the bonding pads and light emitting regions are positioned and mounted on the substrate according to the positioning marks 1Q1, 1Q63, it is impossible to raise the precision of the interval W more than the forming precision of the bonding pads 1Q1 to 1Q64 of the arrays A1, A2.
So far, generally, the positional deviation amount of the bonding pad and light emitting region is determined by the positioning precision between the mask for forming the light emitting regions and the mask for forming the bonding pads, and it is a large value of .+-.10 .mu.m. Therefore, the interval W may produce a maximum deviation of 20 .mu.m, and the printing quality cannot be improved.
In an optical printer head, multiple light emitting diodes are linearly disposed on a semiconductor substrate to compose a picture element array. Multiple picture element arrays are linearly disposed on the substrate, and desired light emitting diodes are illuminated by a control circuit. Ahead of the picture element arrays, a lens array is disposed. The lens array is formed by disposing bar lenses such as self-focusing lenses in one row or in plural rows. The picture from the picture element array is focused on the photosensitive drum through the lens array.
Here, replacing the photosensitive drum with the original copy and using photo diode or photovoltaic array instead of the light emitting diode array, an image sensor is obtained. In this case, the light from the original copy is focused on the photo diode by the lens array, and the original is read.
FIG. 5, FIG. 6 show the compositions used in mounting of picture element arrays in the prior art. In the drawings, numeral 21 is a substrate, 4 is an adhesive layer applied on the substrate 21, and A1, A2, . . . (collectively indicated by reference code A) are picture element arrays. Moreover, numeral 8 is a collet, 02 is a pneumatic cylinder, 04 is a control circuit of the pneumatic cylinder, 10 is a table for moving the substrate, and 12 is a surface plate.
In the prior art, the adhesive 4 is applied on the substrate 21, and the picture element array A is picked up and mounted by the collet 8. The collet 8 drives so that the picture element array A may contact with the adhesive 4 at a specific pressure. As far as the thickness of the applied adhesive layer 4 is uniform and the pressure of the collet 8 is constant, the thickness of the adhesive layer 4 after mounting is constant, and the distance between the bottom of the picture element array A and the substrate 21 is uniform. This in general is the mounting method of electronic components, but since no consideration is given to the fluctuation of thickness of the picture element array, the surface height of the array is not uniform.
The state of the picture element array A after mounting is shown in FIG. 6. Although the thickness of the adhesive layer 4 is constant, the thickness is not uniform in the picture element array A, and this fluctuation directly appears on the surface height of the picture element array A.
Ahead of the picture element array A (above in drawing), a lens array not shown in the drawing is provided. When using an array of light emitting diodes as the picture element array, unless the surface height of the array A is uniform, the light from the light emitting diodes is not correctly focused on the photosensitive drum, and the picture quality is lowered. When using photodiodes or photovoltaic cells in the picture element array A, unless the height of the array A is uniform, the light from the original is not correctly focused on the photodiode. As a result, the picture reading precision is lowered.
The picture element array A is, after being mounted, connected with the wiring of the substrate 21 by means of wire bonding or the like. Here, if the height of the picture element array A is not uniform, the pattern recognition at the time of wire bonding is difficult.
In an optical printer head, multiple picture elements such as light emitting diodes are formed on the surface of a semiconductor chip to compose a picture element array, and a plurality of picture element arrays are disposed linearly. These light emitting diodes form dots of a composed picture, and it is necessary to keep the interval between a light emitting diode and another light emitting diode correctly at a uniform spacing. If the intervals between the light emitting diodes are not uniform, white streaks displaying nothing or black streaks forming black linear images are produced.
To keep the intervals between light emitting diodes in one array spaced correctly, it is enough to heighten the shape precision of the masks and others used in forming light emitting diodes, which is easy. The problem lies in the interval between an array and another array, and if this interval varies, the interval is not uniform between the final light emitting diode of an array and the beginning light emitting diode of the next array, and white streaks or black streaks appear.
Conventionally, as a countermeasure, the electrode position of the light emitting diode was detected by pattern recognition by means of television camera or the like, and the array was positioned. However, when the electrode is manufactured in a different process from the light emitting diodes, the position of the electrode may be deviated from the center of the light emitting diode. If the position of the electrode is deviated, the mounting position of the next array is deviated, and white streaks or black streaks may be caused.
The prior art has been herein described by presenting an example of optical printer head, but the same problem also occurs in image sensor and other image reading apparatus. Instead of light emitting diodes, when photo detector arrays of photodiodes or photovoltaic cells are used, an image reading apparatus is obtained. Also in such a image reading apparatus, unless the positions of arrays are correctly determined, the interval of the reading position fluctuates, and the reading precision is lowered.